As communication networks are becoming more heterogeneous, signal quality of calls over communication networks, or the “call quality,” is a factor of increasing concern to network operators. The communication networks continue to evolve toward a combination of circuit-switching, packet-switching, and various access methods such as cable, digital subscriber line (DSL), cellular radio, wireless local area network (LAN), and broadband wireless. As this evolution continues, service providers, that is, operators of the communication networks, have greater interest in knowing and being able to quantify the end-to-end call quality over the networks.
Operators may use call quality as a quantitative measure to distinguish their service from that of competitors. Users are more likely to migrate toward service providers that provide better and/or more consistent call quality. Therefore, maintaining consistently high call quality is a factor for reducing turnover of users.
A network operator interested in maintaining good and consistent call quality may monitor and test one or more communication networks via non-intrusive signal quality assessment. Non-intrusive signal quality assessment is based on single-sided monitoring without generating traffic and without injecting a separate reference signal. Non-intrusive assessments may be performed by, e.g., human experts, signal processors, etc. FIG. 1 illustrates conventional non-intrusive signal quality assessments 140 and 160. Non-intrusive assessments 140 and 160 generate subjective mean opinion score 150 and objective mean opinion scores 170, respectively, to indicate levels of signal degradation after input signal 105 has traversed a communication network 110 into output signal 115.
Non-intrusive assessments 140 and 160 generate mean opinion scores 150 and 170 without a separate reference signal, e.g., input signal 105. A human expert may conduct non-intrusive assessment 140 by listening to a phone call with a test device (e.g., a conventional handset) connected in parallel to a phone line. Based on the expert's experience 120, expectation 125, and understanding of semantics 130, the expert may generate a subjective mean opinion score 150 on the perceptual quality of output signal 115. A signal processor may conduct non-intrusive assessment 160 by processing output signal 115. By using one or more processing methods (e.g., signal processing algorithms), the signal processor may generate an objective mean opinion score 170 on the perceptual quality of output signal 115.
Non-intrusive methods for objective measurement and assessment of perceptual quality include the ITU-T P.563 method (P.563 method) and the Single Sided Speech Quality Measure algorithm (3SQMTM). For more information on the ITU-T P.563 method, see “ITU-T P.563: Single ended method for objective speech quality assessment in narrow-band telephony applications,” circulated on May 2004 by the International Telecommunication Union (ITU), the entire contents of which are incorporated herein by reference. For more information on 3SQM, see “3SQMTM: Advanced Non-Intrusive Voice Quality Testing,” published 2003 by OPTICOM GmbH (OPTICOM), the entire contents of which are incorporated herein by reference.
One way for a user to objectively measure the perceptual quality of a voice call from any telephone terminal equipment (e.g., black phone, cell phone, internet protocol (IP) phone, computer, etc) is to dial into or connect to a P.563 server that makes non-intrusive perceptual quality measurements, speak a set of test sentences, and then view the results. An example of a P.563 web service is that provided by the 3SQM web-based server operated by OPTICOM.
OPTICOM presently operates two 3SQM servers, one located in Mountain View, Calif., and the other in Germany. However, OPTICOM's P.563 service generally requires the voice signal from a user's terminal to OPTICOM's server to traverse one or more long-distance communication networks, unless the user's terminal happens to be local to the server. The long distance communication networks may be based on circuit-switching, packet-switching, or a combination thereof. Therefore, the quality measurement obtained from OPTICOM's server may not accurately reflect the call quality that the users experience during local or regional calls.
Accordingly, there is a need for distributed apparatus and methods that measure the perceptual quality of a signal at various points of a communication network. It is desirable that such distributed apparatus and methods provide customers of telecommunications carriers and/or service providers the capability to make more accurate measurements of their call quality to any point in the network of the carriers or service providers.